A substrate transfer system, as a substrate processing system for performing a process of multiple steps on a wafer as a substrate, includes a stocker for stocking therein unprocessed/processed wafers; a plurality of substrate processing apparatuses corresponding to the respective steps; and an RGV (Rail Guided Vehicle) as a substrate transfer vehicle for transferring the wafers between the stocker and each of the substrate processing apparatuses.
Conventionally, a wafer has a small diameter and, therefore, it is taken a short period of time to perform each of the steps for a single wafer. Thus, in view of improving transfer efficiency, the RGV transfers a carrier accommodating therein a plurality of wafers, e.g., 25 wafers, between the stocker and each of the substrate processing apparatuses and loads the corresponding carrier into each of the substrate processing apparatuses.
A recent trend of large diameter wafers has increased the time required for performing the respective steps on the wafer. Accordingly, a substrate transfer system for loading wafers sheet by sheet into each of the substrate processing apparatuses (hereinafter, referred to as ‘single wafer transfer system’) is being widely used. An RGV in this substrate transfer system receives wafers sheet by sheet from the stocker by using a transfer arm mechanism of the RGV and then transfers the received wafers while accommodating them in a buffer of the RGV (see, e.g., Japanese Patent Laid-open Application No. 2005-93690). Further, the RGV unloads the wafers from the buffer by using the transfer arm mechanism and then loads them sheet by sheet into each of the substrate processing apparatuses.
However, the above-described single wafer transfer system has a drawback in that wafer transfer efficiency is difficult to improve due to a large number of operations for accommodating the wafers in the buffer of the RGV and unloading them therefrom, which requires an extended time period. Moreover, since a recent improvement of a processing technique has shortened the time required for performing the respective steps, the operations for accommodating the wafers in the buffer of the RGV and unloading them therefrom bottleneck the improvement of the wafer transfer efficiency in the single wafer transferring system.